The invention relates to improvements in couplings in general, and more particularly to improvements in so-called sleeve couplings which can be utilized to establish a fluid-tight connection between a pair of tubular members, especially between a rigid or substantially rigid tubular member and a flexible tubular member. For example, the rigid tubular member can constitute a piece of metallic pipe or tube, and the flexible tubular member can constitute an elastic hose.
It is already known to provide the external surface of one end portion of a rigid tube with a circumferentially extending rib and to slip one end portion of a hose over the rib so that the hose surrounds a substantial part of the external surface. The dimensions of the tube and hose are normally selected in such a way that, prior to its expansion, the outer diameter of the hose exceeds the maximum diameter of the rib and the inner diameter of the hose is smaller than the outer diameter of the tube in the region of establishment of sealing engagement between the tube and the hose, namely, at one or more locations other than that taken up by the rib. The expanded hose is held against slippage off the tube by a clamping sleeve which is provided with an annulus of elastic prongs alternating with slots extending in parallelism with the axis of the sleeve. The sleeve surrounds the expanded portion of the hose and urges the latter against the rib as well as against that portion of the external surface of the tube which is adjacent to and located at the side of the rib facing toward the inserted free end of the tube. Thus, portions of the prongs surround the rib on the tube.
In accordance with a presently known proposal, the clamping sleeve is configurated in such a way that the inner diameters of its ends are smaller than the inner diameter of its median portion. Furthermore, the inner diameter at one end of the sleeve is smaller than at the other end. The length of the clamping sleeve, as considered in the axial direction of the coupling, is selected in such a way that the (other) end whose inner diameter is larger surrounds a radially outwardly sloping outer side of the rib and the one end of the sleeve surrounds the hose and urges it against the external surface of the tube in a region which is located inwardly of the rib, namely, in a region which is separated from the concealed free end of the tube by the rib which latter extends radially outwardly from the external surface of the tube. Such design of the clamping sleeve ensures that the sleeve bears against the hose with a rather pronounced force at both ends of the sleeve, i.e., the hose is urged against the exterior of the tube with a pronounced force not only at the one end of the sleeve (namely, the end whose inner diameter is smaller) but also at the other end even though the coupling does not employ any screws, bolts or analogous conventional tensioning devices (such tensioning devices are often impractical because their manipulation contributes to the installation or dismantling time of the coupling). All that is necessary is to slip the clamping sleeve onto the end portion of the hose before such end portion is slipped onto the end portion of the tube whereby that end portion of the sleeve whose inner diameter is smaller travels over and beyond the rib.
A drawback of the just described conventional sleeve coupling is that, if the pressure in the interior of the coupling rises beyond a certain value (e.g., if the pressure of a gaseous or hydraulic fluid flowing through the tube and through the hose rises beyond a given limit), the hose is expanded radially outwardly and ultimately slides off the end portion of the tube as soon as the axial components of forces developing during radial expansion of the hose overcome the frictional engagement between the internal surface of the hose and the external surface of the tube. Radial expansion of the hose takes place in a region which is adjacent to the hose portion that is surrounded by the clamping sleeve. Once the end portion of the hose begins to slip along the external surface of the tube, the separation progresses rather rapidly and the axial movement of the hose relative to the tube is shared by the clamping sleeve since the latter is not in direct engagement with the tube.